It is previously known in this art how artificial implants may be anchored directly in bone tissue. In order to avoid the risk of loosening or detachment, every attempt is made to achieve a direct contact, that is an exact adaptation between the implant and the surrounding bone tissue, so-called osseointegration. Such an exact adaptation may be achieved by sophisticated operational technique and by a suitable design of the implant. The osseointegration principle developed by professor Branemark et al has successfully been used clinically for 20 years for maxillary-anchored dental bridges and is described in, for example:
P-I Branemark et al, "Osseointegrated titanium fixtures in the treatment of edentulousness". Biomaterials, 1983. Vol 4, January; and Rickard Skalak, "Biomechanical considerations in osseointegrated prostheses". The Journal of Prosthetic Dentistry, June 1983, Volume 49, Number 6.
The principle is based on the fact that the implant is of pure titanium, at least in the interface zone between living tissue and implant. Swedish patent specification No. 79.02035-0 corresponding to U.S. Pat. No. 4,330,891 also discloses and describes the importance of the surface structure of the titanium for a powerful connection between the living bone tissue and the implant. By a special so-called microporous surface structure of the implant, the preconditions are further improved for a more or less permanent anchorage of the implant in the tissue.
To be able to assess the preconditions and potential for different implants to form a permanent anchorage with the tissue, there is a need to be able to study in greater detail and under standardized conditions the bone ingrowth of the implant and also those phases which precede the bone formation itself. Thus, it is previously known in this art how a special examination chamber may be operated into the bone tissue of a living animal, the chamber being designed such that samples of newly-formed bone tissue may be harvested from the chamber at regular intervals, and be examined. Hence, the chamber makes possible a quantification of bone ingrowth/implant incorporation under different experimental conditions without the need of sacrificing the animal. Such a test chamber, "The Harvest Chamber", is described in
T. Albrektsson, M. Jacobsson and P. Kalebo, "The Harvest Chamber--A newly developed Implant for Analysis of Bone Remodelling in situ", Biomaterials and Biomechanics 1983, pp. 283-288.
From such disclosures as the above-mentioned Swedish patent specification No. 79.02035-0, it is apparent that certain substances possess bone growth promoting properties, for example they increase or hasten the growth of bone tissue into an implant and, by such means, shorten the healing time required for the implant. However, prior art methods for studying the effects of such various substances on bone growth have not been without their problems. First, it is difficult to administer a potentially bone-stimulating substance locally and, moreover, it is no easy matter to establish that such a substance actually reaches the tissue which is to be examined. Secondly, the evaluation of the new tissue formed once the substance has been added requires with all certainty that the newly-formed bone tissue can be distinguished from existing bone tissue. A number of solutions to these problems have been proposed earlier. For example, biomechanical tests have been employed to examine the effects of prostaglandin on animal bone tissue. Furthermore, scintigraphic methods have been employed to investigate hormonal growth promoting properties on demineralized cortical bone. Methods based on tetracycline treatment are also previously known in the art.